Electronic musical instrument employing a sampling system as a coupler

ABSTRACT

An electronic musical instrument employing a sampling system as a coupler for obtaining a musical tone by coupling a plurality of tone signals together. The system includes sampling circuits each adapted for sampling with a control signal an input signal applied from a corresponding tone generator which generates a tone signal or from a corresponding envelope circuit which delivers a depression- responsive signal in response to closure of a key switch of the musical instrument, square waveform voltage generators each generating a square waveform voltage as the control signal to the sampling circuit, and duty ratio varying circuits connected to respective square waveform voltage generators for varying the duty ratio of the square waveform voltage so as to vary the magnitude of the output signal of the sampling circuit.

United States Patent [191 I Tsukamoto'et al.

15 1 ELECTRONIC MUSICAL INSTRUMENT EMPLOYING A SAMPLING SYSTEM AS A COUPLER 7 [75] inventors; MasaoTsukamoto, Moriguchi;

Tomiii Munehiro, Neyagawa, both Related U.S. Application Data [63] Continuation of Ser. No. 69,397, Sept. 3, 1970,

abandoned.

[30] Foreign Application Priority Data Sept. 9, 1969 Japan 44 72453' [52] U.S. Cl 84/1111, 84/l.1, 84/1.17, I 84/122,- 84/127 [51] Int. Cl. G101! 1/06 [58] Field of Search 84/101, 1.09-1.12,

84/1.19-l.23, 1.25, DIG. 4, 1.17, 1.27

[451 Nov, 27, 1973 7/1966 Krug 84/l.25 3,510,565 .5/1970 Morez 84/125 X 3,520,982 7/1970 M'almfors 84/ 1.01 3,532,799 10/1970 'Kameoka et al.... 84/1.12 3,598,892 8/1971 Yarnashita 84/l.01 3,602,824 8/1971 Rusch et al. 84/l.01 X 3,637,913 1/1972 Evans 84/l.0l 3,651,242 3/1972 Evans 84/1.1 1

Primary Examiner-Richard B. Wilkinson Assistant Examiner-Stanley J. Witkowski Attorney-Stevens et al.

[57] ABSTRACT An electronic musical instrument employing a sampling system as a coupler for obtaining a musical tone by coupling a plurality of tone signals together. The system includes sampling circuits each adapted for sampling with a control signal an input signal applied from a corresponding tone generator which generates a tone signal or from a corresponding envelope circuit which delivers a depression-- responsive signal in response to closure of a key switch of the musical instrument, square waveform voltage generators each generating a square waveform voltage as the control signal to the sampling circuit, and duty ratio varying circuits connected to respective square waveform voltage generators for varying the duty ratio of the square waveform voltage so as to vary the magnitude of the output signal of the sampling circuit. 1

8 Claims, 20 Drawing Figures [56} References Cited UNITED STATES PATENTS 2,480,137 8/1949 l-loughton...;.. ..s4/1.21'x

3,006,228 10/1961 White ..84/1.01 3,007,361 11/1961 Waynel ..84/l.01

4FT TONE SIGNAL R1 3 R2 R3 20 D1 lcl T TONE 4FT c NTR L 8F SIGNAL, 3 glGN L RI 2 Zbg c NT RO 16FT TONE 8FT SIGN/LL 3 @84 2 V R2 3 ONTROL n CSIGNAL PMENTEDnuvz 1m 3775545 SHEETEOF s FIG. 6

' 4FTTONE SIGNAL. RI 3R2 R3 BFT TONE 4FT c NTR L SIGNL 3 |eN2:

J; 3 m v 20 1 T T 4FT- CONTROL SIGNAL DI :3 SIGNAL 2% y R4 IGFT TUNE O SIGNA DI 3 I El OUT PUT FIG. 7]

A. I R: 2 IGFTCONTROL SIGNAL 'PAIENTEDHDYZTISB 3775545 swam 8 H QW Q 1 BASE VOLTAGE OF Tri BASE VOLTAGE OF Tr2 F|G.l7b

' W W W k K I k v I fiME fly";

I FlG.I'(da TIME ELECTRONIC MUSICAL INSTRUMENT EMPLOYING A SAMPLING SYSTEM As A {COUPLER This is a continuation, of application Ser. No. 69,397,

filed Sept. 3,, 1970, nowabandoned.

This invention relates to a coupler system for use in an electronic musical instrument such as an electronic organ for producing simultaneously the tones spaced apartby octave relation in the same keyboard or the same tones or tones spaced apart by octave relation in a plurality of keyboards such as an upper and a lower keyboards. More particularly, the present invention relates to a coupler system which takes advantage of the pul'setec'hnique so that the degree or mixing of a plurality of tones to be coupled together can be varied as desired.

It is an object, of the present invention to provide a system capable of easily varying the degree of coupling of tones. e 1

Another object of the present invention is to provide a-sysem capable of easily varying'the degre'e of coupling of tones in an electronic musical instrument of the direct keyingtypein which'the transmission of a tone signal to the following circuit is directly controlled by A further object ofthe present invention is to provide a system capable of easily varying the degree of coupling of tones in. an electronic musical instrument of the indirectke ying type in which the transmissionof a tone .signal to the following circuit is indirectly controlledby controllinga gate by a control signal obtained in re sponse to manipulationof a key switch.

A still further'objectof the present invention is to provide, in an electronic'musical instrument of the indirectkeying typehaving two or morekeyboards, a sys-. tem in-which, inresponse to depression of a key switch in'one of;the keyboards for producing a tone, a tone same asthe tone produced by the depression of the key switch or a tone in octave relation with the above tone can be simultaneously produced from another keyboard, and yet the degree of coupling of these tones can be easily varied. r

A yet further object of the present invention is to provide a system capable of easily varyingthe degree of coupling oftones in an electronic musical instrument of the indirect keying type provided with a touchsensitive function so that the volume of a tone is variable depending on the rate of depression of the key of a key switch, that is, the intensity of striking the key.

These and other objects, features and advantages of the present invention will be madeclear from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying some embodiments of the present invention preferably used in an electronic musical instrument of the direct keying type;

FIG. is a block diagram of parts of an embodiment I of the present invention preferably used in an electronic musical, instrument of the indirect keying type;

2 FIGS.'11,-'l2 and 13 are graphic representations of signal waveforms for illustrating the operation of the embodiment shown in FIG. 10;

FIG. 14 is a block diagram of parts of another embodiment of the present invention preferably used in an electronic musical instrument of the indirect keying yp t' FIG. 15 is a circuit diagram of a touch-sensitive effect circuit preferably used in the system according to the present invention;

I FIG. 16 is an example'of a circuit diagram of a square waveform generator for generating a square waveform whose duty ratio is variable; and

FIGS. 17a, 17b, 17c and 17d are graphic representations of signal waveforms appearing at various parts of the generator shown in FIG. 16.

A sampling means employed in the present invention will be described with reference to FIGS. 1 to 5 before giving detailed description as' to application of a coupler system of the present invention to an electronic musical instrument of the direct keying type.

Referring to FIG. l, resistors R, and R are connected in series between an input terminal 1 and an output terminal 4, and a diode D, is connected between a control terminal 2 and the junction point 3 of. the resistors R, and R while a capacitor C, is connected between the output terminal 4 and ground. A tone signal e,.having a waveform as shown in FIG.:2 is applied to the input terminal 1 of the sampling means having a structure as shown in FIG. 1. A control signal e having a waveform as shown in FIG. 3 is applied to the control terminal 20f the sampling means. The control signal e has a repetition frequency sufficiently higher than the frequency of the tone signal e, and the maximum value V,- of the control signale is greater than the maximum value V, of the tone signal e,. Now, the signal appearing at the junction point 3 between the diode D, and the resistors R, and R, will be discussed. When the maximum voltage V is applied to the control terminal 2, the diode D, is reverse biased and is not conducting due to V, V, so that the tone signal applied to the input terminal 1 is passed through the resistor R, to appear at the junction point 3. Then, when the voltage applied to the control terminal 2 is reduced to zero volt, the diode D, is forward biased to conduct and the voltage at the junction point 3 is forcedly reduced to zero volt. In this manner, the diode D, is turned on and off at the same frequency as the repetition frequency of the control signal e applied to the control terminal 2, and as a result, a signal e 'having a waveform as shown in FIG. 4 appears at the junction point 3. The signal e having such a waveform is integrated by the resistor R, and the capacitor C, so that a signal e, having a waveform as shown in FIG. 5 which is analogous to the waveform of r the tone signal e, applied to the input terminal I appears at the output terminal 4. It will be seen from FIG. 5 that the amplitude of the output signal e, can be varied by varying the duty ratio r/T of the control signal Referring to FIG. 6 showing an embodiment of the present invention, a plurality of such circuits are provided for a 4-ft. tone signal, an 8-ft. tone signal and a l6-ft. tone signal, respectively. Outputs of these circuits are connected to mixing resistors R and R, and then to ground through a DC blocking capacitor C and a charging resistor R The junction point between the capacitor C, and the resistor R, is connected to a appearing'at the movable contact 6 of the key switch can be regulated entirely independently of each'other -on the basis of the principle describedabove.

FIG. 7 shows another embodiment of the present invention in which the relative position of the resistor R and the diodeD shown in'FIG. 6 is interchanged so that the diode D is disposed in the-path of each of the 4-ft., 8-ft. and l6-ft. tone signals. The embodiment shown in FIG. 7 is based on the entire same principle as that of the embodiment shown in FIG. 6. Herein, the relation described with reference to FIG. 1 also holds between the tone signal and the control signal. When the voltage V (V V,) is applied to each of the control terminals 2a, 2b and 2c, the diode D is forward biased to conduct so that the tone signal applied to the input terminal appears at the junction point 3 between the diode D, and the resistors R and R Then, when the voltage applied to the control terminal 2 is reduced to'zero volt, the diode D isreverse biased to be cut off so that no tone signal appears at the junction point 3.

Thus, the diode D is turned on and off with the same frequency as the repetition frequency of the control signal applied to the control terminal 2. As a result, signals having a waveform as shown in FIG. 4 appear at the junction point 3 as in the case of FIG. 6.

While the embodiments shown in FIGS. 6 and 7 are so arranged that the 4-ft., 8-ft. and l6-ft. tone signals are sampled relative to the time axis and are then integrated and mixed, these tone signals may be sampled relative to the time axis and then mixed and integrated as shown in FIGS. 8 and 9 to obtain the result similar to FIGS. 6 and 7. This latter case is advantageous in that the number of circuit elements can be reduced compared with the former case.

It will be understood from the above description that the present invention provides many advantages when it is used in an electronic musical instrument of the direct keying type. That is, the system can provide a tone color which is solemn and variable over a wide range due to the fact that the relative intensities of 4-ft., 8-ft. and l6 ft. tone signals can be regulated by a single key switch without the use of a plurality of key switches employed heretofore, and atthe same time, the problems encountered with the. provision of a plurality of contacts including the need for adjustment of the position of these contacts and the reliability of the contacts for attaining the vsimultaneous on-off of a plurality of switches can be completely eliminated. Further, the tone signal is not limited to the sine waveform but it may have any desired waveform such as a square waveform, triangular waveform or saw-tooth waveform.

Another embodiment of the present invention will be described with reference to FIG. 10 to illustrate an application thereof to an electronic musical instrument of the indirect keying type.

Referring to FIG. 10, tone generators 8a, 8b, 8c, 8d and 8e generate tone signals corresponding to the notes C C C C and C respectively. Gate circuits 7a, 7b, 7c, 7d and 7e are connected to the respective tone generators 8a, 8b, 8c, 8d and 8e. Envelope circuits 12a,

12b, 12c, 12d and 12e are provided for the respective gate circuits 7a, 7b, 7c, 7d and 7e and are connected to the respective key switches 13a, 13b, 13c, 13d andl3e. A DC. power supply 14 supplies a DC. voltage to the envelope circuits 12a, 12b, 12c, 12d and 122 through the respective key switches 13a, 13b, 13c, 13d and 13e. 8-ft. sampling circuits 10a, 10b, 10c, 10d and 10e similar to that shown in FIG. 1 are connected between the envelope circuits 12a, 12b, 12c, 12d and 122 and the corresponding gate circuits '7a, 7b, 7c, -7d and 7e, respectively. The control terminals 2 of these sampling circuits 10a, 10b, 10c, 10d and 102 are connected in common to the output terminal of an 8-ft. square waveform generator 16. l6-ft. sampling circuits 11a, 11b, 11c, 11d and lle similar to that shown in FIG. 1 are connected between the envelope circuits 12a, 12b, 12c, 12d and 12e, and a gate circuit (disposed on the lefthand side of the gate circuit 7a) and the gate circuits '7a, 7b, 7c and 7d, respectively. The control terminal 2 gate circuits 7a, 7b, 7c, 7d and 7e, respectively. The

control terminals 2 of these sampling circuits 9a, 9b, 9c, 9d and 9e are connected in common to the output terminal of a 4-ft. square waveform generator 15. The input and output terminals of all these sampling circuits are designated by the reference numerals 1 and 4, respectively. I

In operation, when a desired key is depressed, the envelope circuit corresponding to the depressed key is energized to generate a depression-responsive signal e having a waveform as shown in FIG. 11 and this signal is applied to the sampling circuits connected to the envelope circuit. When, for example, the key switch 13c is turned on, the depression-responsive signal e is applied .to the input terminals 1 of the sampling circuits 9d, and 11c from the envelope circuit 120. Square waveform voltage e as shown in FIG. 3 are applied to the control terminals 2 of the sampling circuits 9d, 10c and 11c from the respective square waveform" generators 15, 16 and 17. The relation V V holds between the maximum value V, of the depression-responsive signal e and the maximum value V of the square waveform voltage e Thus, in response tothe application of the voltage V (V V to the control terminal 2 of each of the sampling circuits 9d, 100 and 11c, the diode D is reverse biased to be cut off so that the depressionresponsive signal applied to the input terminal 1 is passed through the resistor R to appear at the junction point 3 in the manner described with reference to FIG. 1. Then, when the voltage e applied to the control terminal 2 is reduced to zero volt, the diode D, is forward biased to conduct so that the voltage appearing at the junction point 3 is forcedly reduced to zero volt. As a result, a signal e having a waveform as shown in FIG. 12 appears at the junction point 3. A'signal :2, having a waveform as shown in FIG. 13 which is analogous to that of the depression-responsive signal e applied to the input terminal 1 appears at the output terminal 4 when the signal waveform e, is integrated by the resistor R and capacitor C The amplitude of the signal e can be varied by varying the duty ratio r/T of the con- 'trol signal e, appliedf to the control terminal 2. Thus, 'a ccordingto thearrangement shown in FIG. in which the 4-ft., 8-ft. and l6-ft. square waveform generators 15, 1 6 and 17 are-separately providedso that the duty ratios of the'square waveforms can be varied independently of one 'anofther, the depression-responsive signal deliveredfro'mthe envelope circuit 120 and applied'to'thesampling circuits 9d; 100 and He is transformed according tothe duty ratios of the square waveforms supplied from the 7 square waveform generators 5 15, "16 and 17,- and .the transformed signals are applied to the associated gate circuits to obtain the tone signals.

Suppose,-for'example, thatthe duty ratio of the square wave-forms supplied from the 4 ft., 8?ft. and l6-ft. "squ'arewaveform generators 15, 16 and 17 are 1, O and iyrespectively. Then in response to the depression of "the key'switch 13c, the envelope circuit 120 associated with the key switch 13c is" energized to apply the signal corresponding to the note C does not appear.

The depression-responsive signal passed through the l6-ft; sampling'circuit 11chas an amplitude corresponding to -r/'I= k which is the half of the amplitude of the signal passed through the 4-ft. sampling circuit 9d."As a-result, the gate circuit 7b for the note C is half opened to deliver'the tone signal corresponding to the note C but thistone'signal has an amplitude which is l half of the amplitude of' the tone signal corresponding to the note C.,.

It will be understood from the above description that the presentinvention provides many advantages when it is applied to an electronic musical instrument of the indirect keying type. Thatis, a single switch insteadof a plurality of keyswitches can attain-the desiredcouplingof tone signals,'and the number of gate circuits may merely-be equal to the number of tone sources in contrast to the prior art method in whichthe gate circuits whose number' is equal to the number of feet are required for each key switch. Further, the present invention eliminates the priordefect'of ineapability of independently adjusting "the volume of the respective ffeet." According to the present invention, the volume of 'therespective feetcan be continuously varied by varying the duty ratio'of the square waveforms used for the sampling of the depressiomrespective signal. Thus, all theproblems encountered with the provision of a plurality of'contacts including the need for adjustment of the position of these contactsfor attaining the simultaneous on-off of a plurality of contacts, the reliability of the contacts and the high cost due to the complex structure can be solved without degrading the perform- "ance of the musical instrument; In the arrangement -'shown in FIG. 10, the integrating capacitor C (FIG. 1) is incorporated in each of the sampling circuits so as to carry out theintegratio'ri'in each sampling circuiLI-Iowever, the capacitor Cfiin the circuit shown in FIG. 1

may be- 'removed and connected to the output side of a plurality of such sampling circuits so as to reduce the number of parts.

An embodiment of -a keyboard coupler system according to the present invention will be described with reference to FIG. 14. Referring to FIG. 14, the stationary contacts of a key switch 24 is an upper keyboard 23 and a key switch 24 in a lower keyborad 23' are connected to the positive terminal of a DC. power supply 1 l4-whose negative terminal is grounded. The movable contacts'of the key switches 24 and 24' are connected to an envelope circuit 28 associated with the upper keyboard 23 and an envelope circuit 28' associated with the lower keyboard 23, respectively.

The envelope circuit 28 is connected to a resistor R and to the input terminal 1 of a sampling circuit 25 connecting the circuit of the upper keyboard 23 to the circuit of the lower keyboard 23. The envelope circuit 28 is connected to a resistor R and to the input terminal 1 of a sampling circuit 25 connecting the circuit of the lower keyboard 23 to the circuit of th upper keyboard 23. Square waveform generators 29 and 29' generating a square waveform voltage as shown in FIG. 3 are connected to the control terminals 2 and 2' of the sampling circuits 25 and 25', respectively. The square waveform generators 29 and 29' are grounded at the other terminal thereof. The sampling circuits 25 and 25' have a structure as shown in FIG. 1 The output terminal 4 of the sampling circuit 25 is connected to the resistor R and to the control terminal of a gate circuit 27 associated with the lower keyboard 23', while the output terminal 4' of the sampling circuit'25, is connected to the resistor R and to the control terminal of a gate circuit 27 associated with the upper keyborad 23; A tone signal is supplied to the input terminal of the gate circuit 27 associated with the upper keyboard 23 from a tone generator 26, while another tone signal is supplied to the input terminal of the gate 27' associated with the lower keyboard 23' from a tone' generator 26.

. When a required voltage appears at the control termision-responsive signal as shown in FIG. 11 is applied from the envelope circuit 28 to the control terminal of the gate circuit 27 through the resistor R As a result, the gate circuit 27 is opened and the tone signal supplied from the tone generator 26 appears at the output terminal 30 of the gate circuit 27. At the same time, the depression-responsive signal delivered from the envelope circuit 28 associated with the upper keyboard 23 is applied to the input terminal 1 of the sampling circuit 25. In response to the application of the depression- I respective signal having a waveform as shown in FIG.

11 from the envelope circuit 28 and the square waveform voltage having a waveform as shown in FIG. 3 from the square waveform generator 29 to the input terminal 1 and control terminal 2, respectively, of the sampling circuit 25 having a structure as shown in FIG. 1, a waveform as shown in FIG. 12 appears at the junctio nj'point between the diode D and the resistors R .-.and R z due to the on-off of the diode D and is inte- 25. This signal is applied to the control terminal of the gate circuit 27 associated with the lower keyboard 23 to open the gate circuit 27 so that the tone signal supplied from the tone generator 26 appears at the output terminal 30' of the gate circuit 27'. The amplitude of the signal appearing at the output terminal 4 of the sampling circuit 25 can be varied by varying the duty ratio r/T of the square waveform supplied from the square waveform generator 29. It is possible, therefore, to vary theamplitude of the tone signal appearing at the output terminal of .the gate circuit 27 associated with the lower keyboard 23 thereby to adjust the degree of coupling of the tone produced from the lower keyboard 23" to the tone produced from the upper keyboard 23.

When a key in the lower keyboard 23 is depressed to close the key switch 24' corresponding to the key, the voltage-E of the DC. power supply 14 is applied to the envelope circuit 28 associated with the lower keyboard 23. Then, when the force applied to the key is released in a certain period of time, a depressionresponsive signal as shown in FIG. 11 is applied from the envelope circuit 28 to the control terminal of the gate 27 through the resistor R As a result, the gate 27' is opened and the tone signal supplied from the tone generator 26' appears at the output terminal 30' of the gate 27. At the same time, the depressionresponsive signal delivered from the envelope circuit 28 associated with the lower keyboard 23' is applied to the input terminal 1' of the sampling circuit 25'. In response to the application of the depressionresponsive signal having a waveform as shown in FIG. 11 from the envelope circuit 28 and the square waveform voltage having a waveform as shown in FIG. 3 from the square waveform generator 29 to the input terminal 1 and control terminal 2', respectively, of the sampling circuit 25' having a structure as shown in FIG. 1, a signal having a waveform as shown in FIG. 13 appears at the output terminal 4 of the sampling circuit 25 This signal is applied to the control terminal of the gate 27 associated with the upper keyboard 23 to open the gate 27 so that the tone signal supplied from the tone generator 26 appears at the output terminal 30 of the gate 27. In this case too, the amplitude of the signal appearing at the out-put terminal 4' of the sampling circuit 25' can be varied by varying the duty ratio 'r/T of the square waveform supplied from the square waveform generator 29'. It is possible, therefore, to vary the amplitude of the tone signal appearing at the output terminal 30 of the gate 27 associated with the upper keyboard 23 thereby to adjust the degree of coupling of the tone produced from the upper keyboard 23 to the tone produced from the lower keyboard 23'. A keyboard coupler system can thus be realized. The keyboard coupler system based on the above method does not require additional provision of key switches, and therefore, eliminates the problems encountered with the prior art arrangement including the simultaneous on-off of switches, the need for adjustment of the position thereof and the reduction in the reliability of the switches due to the increase in the number of the key switches. Further, the-degree of coupling of the tones produced from the keyboards can be continuously varied by regulating the duty ratio 'r/T of the waveform generated by the square waveform generators.

It will be understood from the foregoing description I that the present invention eliminates many problems as described above encountered with the prior art coupler system when it is applied to electronic musical instruments of both the direct and the indirect keying type. Especially, the coupler system according to the present invention is indispensable in an electronic musical instrument of the kind which will be described below.

An important feature of the sampling circuit forming the essential part of the coupler system according to the present invention shown in FIG. 1 resides in the. fact that the voltage appearing at the output terminal 4 is proportional to the voltage supplied to the input terminal 1 within the range of0 V 2' V (FIGS. 2 and 3), and is also proportional to the duty ratio 'r/T of the square waveform supplied to the control terminal 2. A system utilizing the proportional relation between the output and input voltage will now be described.

Musical instruments presently in use include an instrument such as a cembalo which produces a tone whose volume is constant independently of the strength of touching the key and an instrument such as a piano which produces a tone whose volume is variable depending on the strength of striking the key. While the former musical instrument produces a very delicate and beautiful tone color, it has a drawback that the'volume of the tone does not vary depending on the key striking force, and it is said that the piano is developed to take the place of the cembalo. Looking back to the history of these musical instruments, it is apparent that the future tendency of electronic musical instruments is toward the capability of producing a variable tone volume or tone color depending on the key striking force or key striking rate.

Such a demand can be met by the use of an envelope circuit as shown in FIG. 15 in an electronic musical linstrument of the indirect keying type so that the electronic musical instrument can produce a tone whose volume is variable depending on the key striking rate. Referring to FIG. 15, a key switch includes a normally closed stationary contact 31, a movable contact 32 and a normally open stationary contact 33. In this key switch, the so-called contact transition time required for the movable contact 32 to contact the normally open stationary contact 33 after it is urged away from the contact with the normally closed stationary contact 31 becomes shorter with a higher key striking speed, while the contact transition time becomes longer with a lower key striking speed. The normally closed stationary contact 31 is connected to the negative terminal of a DC. power supply 14, while the normally open stationary contact 33 is connected to the positive terminal of the DC. power supply 14, and at the same time, to ground. The movable contact 32 is connected through a parallel circuit of a capacitor C and a resistor R to an output terminal 34 which is connected to the cathode of a diode D whose anode is grounded. In the position in which the key is not depressed, the capacitor C is charged to E volts from the DC. power supply 14 through the diode D movable contact 32 and normally closed stationary contact 31, with the capacitor terminal connected to the output terminal 34 being positive relative to the other terminal connected to the movable contact 32. Then, when the key is depressed in the above state to urge the movable contact 32 away Y 9 from the normally closed stationary contact 31, the voltage charged in the capacitor C starts to discharge through theresistor R but no voltage appears yet at the output terminal 34.

In a suitable period of time, the movable contact 32 is brought into contact with the normally open stationary contact 33 and the voltage across the capacitorC appears at the output terminal 34. When the transition time for the movable'contact 32 is short, the voltage charged in the capacitor C is not discharged so much through the resistor R and a relatively large voltage appears at the output terminal 34 when the movable contact 32 is brought into contact with the normally open stationary contact 33. When, however, the transition time is long, the voltage charged in capacitor C is sufficiently discharged through'theresistor R and a very small voltage appears at the output terminal 34 when the movable contact 32 is brought into contact with the normally open stationary contact 33. That is, witha high key striking'speed, hence with a short transition time, a large voltage appears at the output terminal 34, while. with a low key striking speed, hence with a long transition time, a small voltage appears at the output terminal 34. The circuit shown in FIG. may be employed in place of the key switches 13a, 13b, 13c, 13d and l3e and the envelope circuits 12a, 12b, 12c, 12d and l2e in the system shown in FIG. 10. It will be recalled that there is a proportional relation between the signal delivered from the envelope circuits 12a, 12b, 12c, 12d and l2e and the signal applied to the gate circuits 7a, 7b,.7'c, 7d ane 7e, that is, there is a proportional relation between the input to and the output from the sampling circuits 9a, 9b, 9c, 9d, 9e; 10a, 10b, 10c, 10d, l0e; and 11a, 11b, 11c, lld,-l1e. Therefore, any variation in the output voltage delivered from the envelope circuits 12a, 12b, 12c, 12d and l2e depending on the key strikingspeed results in the corresponding variation in the signal applied to the gate circuits 7a, 7b, 7c, 7d and 7e so that tonesignals of large amplitude appear at the output terminals of the gate circuits in response to a high key striking speed, while tone signals of small amplitude appear at the output terminals of the gate circuits in response to a low key striking speed. In a coupler system for use in an electronic musicalinstrument in which the amplitude of the depression responsive signal is variable depending on the key striking speed, there must be a linearity between the amplitude of the input and the amplitude of the output. In this respect too, the coupler system according to the present invention is -quite excellent.

The square waveform generator capable of generating a square waveform whose duty ratio 'r/T is variable can be offered in several forms. One form of such square waveform generator is shown in FIG. 16, and this square waveform generator is so arranged as to vary the duty ratio depending on the magnitude of a DC. voltage. Referring to FIG. 16, the square waveform generator includes a differential amplifier composed of two transistors Tr, and Tr When a saw-tooth waveform voltage as shown in FIG. 17a is applied to the base of one of the transistors Tr, and a DC. voltage Va is applied to the base of the other transistor Tr the output appearing at the collector of the transistor Tr;

has a waveform as shown in FIG. 17b from which it will be seen that the portion of the saw-tooth'waveform above the level Va is solely greatly extended. This wavefrom is thenshaped by a Schmitt circuit composed of two transistors Tr and Tr, to obtain a waveform as shown in FIG. 170. The waveform thus obtained is aniplified to a required amplitude and shaped by a transistor Tr the resulting waveform being then passed through an emitter follower including a transistor Tr to obtain a signal as shown in FIG. 17d. It will be appareat, that the duty ratio r/T of the waveform derived from the emitter of the transistor Tr can be continuously varied within the range of 0 to l by varying the DC. voltage Va.

While the foregoing description has referred to a system in which a diode is used as the switching element in the sampling circuit, the switching element is in no way limited to the diode, and a transistor, electronic tube or the like may be employed in lieu of the diode for exhibiting the performance similar to that attained by the sampling circuit; Further, the operation entirely the same as that described above can be carried out by reversing the polarity of all the'circuit components including the diode and power supply. Furthermore, the foregoing description has referred to a coupler system including couplers for the l,6-ft., 8-ft. and 4-ft. tone signals, but it will be readily apparent that the present invention is similarly applicable to a coupler system including couplers for the 32-ft., 2am, I 3/5-ft., l /3-ft l-ft. and other tone signals. Moreover, the present invention includes also a coupler system in which any suitable sampling circuit is employed in lieu of the sampling circuit described in the specification.

What is claimed is:

1. An electronic musical instrument employing a sampling system as a coupler comprising a. a plurality of tone generators each having an output terminal at which a tone signal is generated,

b. a plurality of square waveform voltage generator each having an output terminal at which a square waveform voltage having a predetermined amplitude and repetition frequency is generated, said square waveform generators including duty ratio varying means for varying the duty ratio of said square waveform voltage,

c. a pluralityof sampling means each having input output and control terminals, the input terminal of each of said sampling means being coupled to a corresponding one of said tone generators, the control terminal of each of said sampling means being coupled to a corresponding one of said square waveform voltage generators, the signal generated at the output terminal said sampling means having a frequency corresponding to the signal applied to the input terminal but having a magnitude an amplitude determined by the duty ratio of the coupled square waveform voltage generator,

d. a plurality of coupling means each having at least two inputs respectively coupled to the output terminals of at least two of said sampling means and an output, and

e. means for obtaining a musical tone by receiving the signal at the output of said coupling means.

2. An electronic musical instrument as claimed in claim 1, which further comprises integrators connected between respective said sampling means and said coupling means and in which the sampled tone signal derived from said sampling means is supplied to said means for obtaining a musical tone through said integrator together with other sampled tone signals to be coupled with said tone signal.

sampling means are coupled together to be supplied to said means for obtaining a musical tone through said common integrator.

4. An electronic musical instrument as claimed in claim 1, in which said square waveform voltage has an amplitude greater than the maximum amplitude of said signal to be sampled.

5. An electronic musical instrument employing a sampling system as a coupler comprising a. a plurality of tone generators each having an output terminal at which a tone signal is generated,

b. a plurality of square waveform voltage generators each having an output terminal at which a square waveform voltage having a predetermined amplitude and repetition frequency is generated, said square waveform generators including duty ratio varying means for varying the duty ratio of said square waveform voltage,

c. a plurality of sampling means each having input,

- output and control terminals, the control terminal of each of said sampling means being coupled to a corresponding one of said square waveform voltage generators, the signal generated at the output terminal of said sampling means corresponding to the signal applied to the input terminal but having a magnitude determined by the duty ratio of the coupled square waveform voltage generator,

d. a plurality of coupling means each having at least two inputs respectively coupled to the output terminals of at least two of said sampling means and an output terminal, and

e. a plurality of envelope circuits each having an input terminal connected to a corresponding one of a plurality of key switches and an output terminal connected to the input terminals of at least two of said sampling means for delivering a depression responsive signal in response to' closure of said key switch for applying said depression-responsive signal to said sampling means as said input signal,

minal coupled to a coresponding one of said tone generators, an output terminal, and a control terminal connected to the output of a corresponding one of said coupling means for controlling the transmission of said tone signal to the output terminal of said gate means in response to the sampled depression-responsive signal, and

g. means coupled to the output terminals of said gate means to derive musical tones from the signals generated by said tone generators and passed by said gate means.

6. An electronic musical instruments as claimed in claim 5, in which said envelope circuits are disposed in each section of a keyboard which is divided into at least two sections, and said sampling means are disposed in the depression-responsive signal transmission passages corresponding to the tone signals to be coupled together thereby attaining the coupling of the tone signals produced from the divided keyboard sections.

7. An electronic musical instrument as claimed in claim 5, in which each of said envelope circuits includes means for varying the magnitude of the signal output depending on the speed with which the key is depressed.

8. An electronic musical instrument as claimed in claim 5, n which said square waveform voltage has an amplitude greater than the maximum amplitude of said signal to be sampled.

a plurality of gate means each having an input ter- 

1. An electronic musical instrument employing a sampling system as a coupler comprising a. a plurality of tone generators each having an output terminal at which a tone signal is generated, b. a plurality of square waveform voltage generator each having an output terminal at which a square waveform voltage having a predetermined amplitude and repetition frequency is generated, said square waveform generators including duty ratio varying means for varying the duty ratio of said square waveform voltage, c. a plurality of sampling means each having input output and control terminals, the input terminal of each of said sampling means being coupled to a corresponding one of said tone generators, the control terminal of each of said sampling means being coupled to a corresponding one of said square waveform voltage generators, the signal generated at the output terminal said sampling means having a frequency corresponding to the signal applied to the input terminal but having a magnitude an amplitude determined by the duty ratio of the coupled square waveform voltage generator, d. a plurality of coupling means each having at least two inputs respectively coupled to the output terminals of at least two of said sampling means and an output, and e. means for obtaining a musical tone by receiving the signal at the output of said coupling means.
 2. An electronic musical instrument as claimed in claim 1, which further comprises integrators connected between respective said sampling means and said coupling means and in which the sampled tone signal derived from said sampling means is supplied to said means for obtaining a musical tone through said integrator together with other sampled tone signals to be coupled with said tone signal.
 3. An electronic musical instrument as claimed in claim 1, which further comprises a common integrator connected between said coupling means and said means for obtaining a musical tone and in which said sampling means are provided for respective said tone signals to be coupled toGether so as to receive said tone signal, and the sampled tone signals derived from said sampling means are coupled together to be supplied to said means for obtaining a musical tone through said common integrator.
 4. An electronic musical instrument as claimed in claim 1, in which said square waveform voltage has an amplitude greater than the maximum amplitude of said signal to be sampled.
 5. An electronic musical instrument employing a sampling system as a coupler comprising a. a plurality of tone generators each having an output terminal at which a tone signal is generated, b. a plurality of square waveform voltage generators each having an output terminal at which a square waveform voltage having a predetermined amplitude and repetition frequency is generated, said square waveform generators including duty ratio varying means for varying the duty ratio of said square waveform voltage, c. a plurality of sampling means each having input, output and control terminals, the control terminal of each of said sampling means being coupled to a corresponding one of said square waveform voltage generators, the signal generated at the output terminal of said sampling means corresponding to the signal applied to the input terminal but having a magnitude determined by the duty ratio of the coupled square waveform voltage generator, d. a plurality of coupling means each having at least two inputs respectively coupled to the output terminals of at least two of said sampling means and an output terminal, and e. a plurality of envelope circuits each having an input terminal connected to a corresponding one of a plurality of key switches and an output terminal connected to the input terminals of at least two of said sampling means for delivering a depression-responsive signal in response to closure of said key switch for applying said depression-responsive signal to said sampling means as said input signal, f. a plurality of gate means each having an input terminal coupled to a coresponding one of said tone generators, an output terminal, and a control terminal connected to the output of a corresponding one of said coupling means for controlling the transmission of said tone signal to the output terminal of said gate means in response to the sampled depression-responsive signal, and g. means coupled to the output terminals of said gate means to derive musical tones from the signals generated by said tone generators and passed by said gate means.
 6. An electronic musical instruments as claimed in claim 5, in which said envelope circuits are disposed in each section of a keyboard which is divided into at least two sections, and said sampling means are disposed in the depression-responsive signal transmission passages corresponding to the tone signals to be coupled together thereby attaining the coupling of the tone signals produced from the divided keyboard sections.
 7. An electronic musical instrument as claimed in claim 5, in which each of said envelope circuits includes means for varying the magnitude of the signal output depending on the speed with which the key is depressed.
 8. An electronic musical instrument as claimed in claim 5, n which said square waveform voltage has an amplitude greater than the maximum amplitude of said signal to be sampled. 